1. Field of the Invention
The present invention relates to a light focusing optical system having so-called compatibility in which light for recording to and/or reproducing from a plurality of optical recording media of different kinds is focused onto the optical recording media by using a diffraction element and lens, and particularly relates to a light focusing optical system capable of excellently performing aberration correction on the plurality of recording media of different kinds, and to an optical pickup device and optical recording and reproducing device using this light focusing optical system.
2. Description of the Related Art
In recent years, optical recording media of various types having different recoding densities have been developed, and in case of a disk-shaped optical recording medium, for example, those such as a CD (Compact Disk) using a wavelength of laser light around 780 nm, a DVD (Digital Versatile Disc) using a wavelength thereof around 660 nm, a BD (Blu-ray Disc) using a wavelength thereof around 405 nm, and similarly a HD DVD (High Definition DVD) and AOD (Advanced Optical Disk) using a wavelength around 405 nm, for example, can be mentioned.
In these optical recording media, structures thereof differ from each other, and particularly a thickness of a cover portion on the side irradiated with light, that is, the thickness of a substrate and cover layer differs.
In order to obtain a configuration having compatibility for recording to and/or reproducing from such optical recording media of plural kinds in one optical recording and reproducing device, it is necessary to correct optical aberration in the optical system in consideration of such differences in the thickness of the cover portion and in the wavelength of the irradiated light.
For this purpose, a plurality of objective lenses suitable for respective optical recording media may be provided without difficulties (for example, refer to Patent reference 1).
In a method disclosed in the above-described Patent reference 1, as an optical system having compatibility between a DVD and CD, the one in which two objective lenses suitable for the DVD and CD respectively are installed in one bobbin of a biaxial actuator has been put into a practical use.
However, when a plurality of objective lenses are installed, the biaxial actuator becomes large and there is a disadvantage in the aspects of high-speed operation and miniaturization of an optical system.
Then, a method for recording to and reproducing from a plurality of optical recording media of different kinds by using one objective lens has been proposed.
In an optical recording and reproducing device having the compatibility between the DVD and CD, the aberration caused by the differences in the thickness of the cover portion and in the wavelength is corrected by using a diffractive lens (for example, refer to the Patent reference 2).
[Patent reference 1] Japanese Patent Application Publication No. 2001-110086
[Patent reference 2] Japanese Patent Application Publication No. 2001-160235